1. Field of the Invention
Embodiments of the present invention relate to a sheet positioning device to adjust the position of a sheet member or a recording sheet placed on a sheet setting plate at a predetermined position, a sheet holding receptacle incorporating the sheet positioning device, an image forming apparatus incorporating the sheet positioning device, and an image reading device incorporating the sheet positioning device.
2. Description of the Related Art
Known sheet positioning devices adjust a recording sheet placed on a sheet setting plate to a predetermined position in a direction orthogonal to a direction in which the recording sheet is fed to and from the sheet setting plate. Two side fences serving as regulating members are mounted on the sheet setting plate to slide in the orthogonal direction of the sheet setting plate. A sheet contact detector is mounted on each of the side fences to detect contact of the side fence with the recording sheet.
These side fences are located at respective home positions separate from each other in a widthwise direction across a gap having a width greater than the width of a recording sheet. When setting the recording sheet on the sheet setting plate, a driving unit drives to move the side fences to the home positions. While the side fences stay at the home positions, an operator places the recording sheet on the sheet setting plate and issues instructions to slide the side fences toward the center portion in the widthwise direction of the sheet setting plate. When one of the two side fences, e.g., a first side fence, reaches a contact position at which the first side fence contacts the side edge of the recording sheet, the recording sheet contacts the sheet contact detector of the first side fence. With this action, the sheet contact detector detects the contact of the first side fence with the recording sheet. However, the other side fence, e.g., a second side fence, has not yet reached its contact position with the recording sheet.
As the driving of the two side fences continues, the first side fence in contact with the recording sheet slides toward the second side fence while pressing the recording sheet. Thereafter, when the recording sheet that is pressed by the first side fence reaches a contact position at which the second side fence contacts the other side edge of the recording sheet, the recording sheet contacts the sheet contact detector of the second side fence, thereby detecting the contact of the recording sheet with the second side fence. After the contact of the recording sheet with the two side fences has been thus detected, the driving unit stops to stop movement of the side fences. At this time, the recording sheet on the sheet setting plate is aligned at the center of the sheet setting plate in the orthogonal direction.
Japanese Patent Application Publication No. 2001/171893 (JP-2001-171893-A) discloses a sheet positioning device included in an image forming apparatus that aligns the position of a recording sheet by slidably moving two side fences. FIG. 1 is an enlarged perspective view illustrating a part of the sheet positioning device. The sheet positioning device feeds a recording sheet placed on a sheet setting plate 951 in a direction indicated “x” in FIG. 1. Even though FIG. 1 shows only the first side fence 953 of the two side fences, a second side fence is also mounted on the sheet positioning device. As a driving unit drives, while holding a movable switch 954 that serves as a sheet contact detector, the first side fence 953 starts to slide in an orthogonal direction that is a direction perpendicular to a sheet conveying direction indicated “y” in FIG. 1. With the sliding of the first side fence 953, the second side fence also slides toward the first side fence 953. The second side fence holds a movable switch having the same function as that of the first side fence 953. After the two side fences have reached a position at which the recording sheet presses the respective movable switches, the driving unit stops the sliding of the side fences to align the recording sheet at the center of the sheet setting plate 951 in the orthogonal direction or the “y” direction.
However, the sheet positioning device cannot stop the side fences at appropriate positions if one or both edges of the recording sheet in the orthogonal direction are curled.
Specifically, one edge of a recording sheet S in the orthogonal direction may be curled upward, as shown in an example illustrated in FIG. 2. With the curled end, the recording sheet S cannot contact a movable switch 954 when the side fence 953 slides to the contact position with the recording sheet S, but contacts an upper portion, of the side fence located above the movable switch 954. At this time, even if the second side fence correctly contacts the recording sheet S as shown in FIG. 3, the contact of the first side fence with the recording sheet S cannot be detected, which causes the driving unit to continue to move the side fences. If the side fences move further, the edge of the recording sheet S does not contact the movable switch 954 and the recording sheet S warps, as illustrated in FIG. 4. Accordingly, the movement of the side fences continues further without detecting the contact of the recording sheet S with the first side fence 953 until they reach the limits of their movement in the orthogonal direction “y”. Accordingly, the sheet positioning device of JP-2001-171893-A cannot align the recording sheet S properly.